The present invention relates to a zoom lens-barrel assembly, and in particular to a zoom lens-barrel assembly having more than two lens groups.
Recently, various mechanisms for driving a zoom lens have been proposed in connection with the automatization of camera. For example, Japanese Patent Publication Sho/39-15721 discloses a lens barrel having a zoom lens driving mechanism which is a combination of a helicoid screw and a differential cam. Japanese Laid-Open Patent Application No. 59-148012 discloses a zoom lens assembly which is adapted to drive a zoom lens by cam-linking first and second zoom lens holding frames with each other. Japanese Laid-Open Utility Model Application Sho/62-201710 discloses a lens driving mechanism in which a cam slot for driving a lens is provided by biasing first and second cam members to an engaging pin in a barrel. A mechanism for driving a lens frame in a barrel which was proposed in pending Japanese Patent Application Sho/63-33029 filed by the present assignee is of a cam ring type.
Driving a number of lens holding frames by using the afore-mentioned lens driving mechanism of a barrel offers disadvantages such as complicated structure an the problem of molding due to rigidity.
For example, a barrel mechanism for a variable focal point lens disclosed in Japanese Patent Publication No. Sho/39-15721 differentially moves two lens frames. Application of this mechanism to driving of more than two lens frame groups increases the number of components and provides a very complicated structure.
As mentioned above, the lens driving mechanism disclosed in Japanese Patent Application Sho/63-33029 is of the cam ring type. The structure of this mechanism will be described by way of a set of lens frame driving mechanism shown in FIG. 6. A driving barrel 41 has tilted cam slots 41a equally spaced on the outer periphery thereof. A lens holding frame 42 is fitted into the driving barrel 41. The lens holding frame 42 has engaging pins 42a which are fitted in the cam slots 41a. In the thus formed driving mechanism, rotation of the driving barrel 41 causes the lens holding frame 42 to be selectively moved forwardly and rearwardly in an axial direction, so that the lens is moved for zooming. However the cam barrel of this structure requires a high precision. If the cam barrel is made of a plastic material, the cam barrel will deform due to an insufficient rigidity when the driving barrel is subject to an external force so that intended precision cannot be assured. Accordingly, molding of these barrel is impossible. One lens holding frame is driven by three engaging pins. Assuming that the driving mechanism be used for driving three lens groups, a total of nine engaging pins should be screwed into the frame. Accordingly, it is difficult to assemble a zoom lens-barrel assembly having such a driving mechanism.